Questions on Nuclear fusion & fission

(b) t_½ = (ln 2) / λ = 0.693 / λ so λ = 0.693 ÷ 23.5 = 0.0295 min^-1
N = N_oe^−λt so N / N_o = e^{−(0.0295 x 141)} = 0.0156
Percentage remaining = (N / N_o) x 100 = 1.56%.

This can more easily be solved by inspection.
141 minutes is equal to 6 half-lives. 1 → 0.5 → 0.25 → 0.125 → 0.0625 → 0.03125 → 0.0156 (i.e. 1.56 %)

(c) Three neutrons produced since:

2. Each element has its own specific absorption spectrum (the opposite to its emission spectrum) formed when electrons are excited from a lower energy level to a higher energy level. Each transition shows up as a black line on what is otherwise a continuous spectrum. (Helium was not known on Earth when its spectral line at 587.6 nm was first observed in the sun during the nineteenth century). By knowing the precise transitions (spectral lines) for each element (e.g. krypton) the spectra from stars can be analysed to see if they are present.

3. (a) It cannot yet be controlled. The plasma has to be contained for long enough to fuse the nuclei together which involves extremely high temperatures. (For the hydrogen bomb the initial temperature is reached by first setting off a nuclear fission reaction). Nuclear fission reactions can be controlled using control rods and moderators at a much lower temperature.

(b) The amount of energy released is greater than a nuclear fission reaction.
The raw fuel (hydrogen and deuterium) is abundant and cheap to obtain.
The process is virtually non-polluting as no radioactive material s produced.

4. (a) Incinerated or buried in landfill sites.

(b) Unless it can be reprocessed for further use it should be vitrified and encased in steel and concrete and then buried deep underground in an area, which is geologically stable.

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